As defined, the AWG device is an integrated optical device that demultiplexes a composite signal such that once the composite signal has been introduced into an input, the demultiplexed signals are obtained at the multiple output ports.
The output at which each of the demultiplexed signals is obtained is determined by the AWG design.
Although a wavelength is the inverse of the frequency, and therefore they are parameters that define the same properties, throughout the description (unless otherwise specified) the term frequency is reserved for acoustic signals and the term wavelength for optical signals.
Describing the basic configuration of an AWG as known in the prior art, it is formed by:
                one or more input ports consisting of optical waveguides,        a number of output ports consisting of optical waveguides,        a first optical coupler for optical input port mixing,        a second optical coupler for the mixing and output of optical output ports,        a set of optical waveguides with increasing lengths connecting the first optical coupler to the second optical coupler so as to enable the multiplexing/demultiplexing of signals transmitted.        
For the sake of simplicity, it is assumed that the AWG device has a single input. The composite signal entering this input is distributed by the first optical coupler over the entire set of optical waveguides with increasing lengths.
The optical signal that travels through each of the guides will reach the second optical coupler. Since each optical guide has a different length, the route will also be different.
The set of optical waveguides with increasing lengths leads to a selection of output ports depending on the frequency of the optical signal due to a phenomenon of constructive interference that causes light to diffract in one port or another.
The fixed length set of guides with increasing lengths means that the mode in which the outputs are distributed depending on the input is already preset at the design stage and that this distribution cannot change during operation.
If instead of a single input, the device comprises more than one input, there is an output distribution for each input. However, the output distribution is also established during the design stage and cannot change during operation.
For instance, if the multiplexed signal is introduced into input port 1, the demultiplexed signal with a wavelength of λ1 will exit through output port 1, signal λ2 will exit through output port 2, signal λ3 will exit through output port 3, and so on. But if the input port of the multiplexed signal is input port 2, the demultiplexed signal with a wavelength of λ1 will exit through output port 2, signal λ2 will exit through output port 3, signal λ3 will exit through output port 4 and so on. So, the relationship between input and output remains preset.
One way to get around this limitation is to modify the refractive index of optical waveguides along which the optical signal travels. This will modify the propagation conditions of light inside the guides and AWG behaviour can change during operation.
The prior art discloses proposals of technical solutions aimed at modifying the refractive index to enable AWG tuning.
In particular, the patent application with publication number US2002/0080715A1 describes and claims a first method for refractive index variation by changing the temperature of the guides.
While this method of varying the refractive index is feasible, the temperature changes are not immediate and require a long transition time. The thermal inertia prevents this change from being almost instantaneous.
This very same application US2002/0080715A1 addresses the possibility of using acoustic waves since they also modify the refractive index. Although this solution is presented generically and is even claimed, the application itself acknowledges that is not feasible since it requires a constant change rate. The patent application does not disclose a solution to this problem.
The present invention solves the above problem by establishing a particular mode of acoustic excitation on the optical waveguides. The result is the tuning of the AWG whose change response is almost instantaneous. The invention also covers various configurations that result in particular devices that benefit from the AWG tuning.